Our European Patent EP-B-0 422 117 discloses a lamp holder which is arranged to be secured to a cable in such a manner as to be a permanent fitting and to give a pressure-tight seal to the cap enclosing the connection to the cable. The lamp holder is thus resistant to tampering and vandalism, and has a very long service life, because the problems arising from corrosion due to moisture ingress do not arise.
The lamp holder comprises a base and a cap, the base having a pair of part-circular lugs upstanding therefrom with outwardly facing detents which engage with a continuous groove around the inner surface of the cap. The locking or retaining surfaces of the groove and the detent extend in a plane normal to the axis of symmetry of the cap, so that there is no tendency for the surfaces to cam apart if an attempt is made to prise the cap from the base. This ensures permanency in the fitting of the cap to the base, but it makes the manufacture of the caps difficult, because conventional plastics molding techniques do not readily permit the formation in such a confined space of the retaining surface which is normal to the direction of withdrawal of an internal molding tool. Thus, it has been necessary to machine the recess into the inner surface of the cap after molding, and this adds significantly to the cost of manufacture.
To permit the groove to be formed during molding of the cap, the surface of the groove engaged by the detents is preferably oblique to the axis of symmetry of the cap, for example at 45.degree., with the corresponding surface of the detent being similarly angled. However, while the cap is still difficult to remove from the base when the components are formed in this way, it has been found that removal is possible, for example by levering the cap off with a screwdriver. One aspect of the present invention seeks to provide an arrangement in which a wholly molded cap can still be permanently locked on to the base.
Certain types of long-life low voltage lamps are presented as a festoon lamp having a generally cylindrical envelope with an electrical connection at each end. The electrical connection consists, in one form of lamp, in a wire loop extending from each end of the quartz or glass envelope. Such lamps are intended to fit into low profile reflector holders having a sprung connector at one or both ends which bears against the wire loop to make the electrical contact, the lamp being held lengthways in line with the base. It is desirable to be able to use such lamps in low voltage lighting systems in accordance with the invention, since they would reduce still further the maintenance required. However, it is necessary for the light to be emitted in all directions, rather than simply through substantially 2.pi. radians as occurs in a flat reflector light with which such lamps are normally associated.
Another aspect of the invention provides a lamp holder which permits such lamps to be held perpendicular to the base, allowing light to be radiated through substantially 4.pi. radians.